Evaluation of electromagnetic dosimetry of wireless systems in complex indoor scenarios with human body interaction

In this work, the influence of human body within the estimation of dosimetric values is analyzed. A simplified human body model, including the dispersive nature of material parameters of internal organs, skin, muscle, bones and other elements has been implemented. Such a model has been included within an indoor scenario in which an in-house 3D ray launching code has been applied to estimate received power levels within the complete scenario. The results enhance previous dosimetric estimations, while giving insight on influence of human body model in power level distribution and enabling to analyze the impact in the complete volume of the scenario.The authors wish to acknowledge the financial support of project FASTER, funded by the Consejería de Industria, Gobierno de Navarra

Viability of Numerical Full-Wave Techniques in Telecommunication Channel Modelling

In telecommunication channel modelling the wavelength is small compared to the physical features of interest, therefore deterministic ray tracing techniques provide solutions that are more efficient, faster and still within time constraints than current numerical full-wave techniques. Solving fundamental Maxwell's equations is at the core of computational electrodynamics and best suited for modelling electrical field interactions with physical objects where characteristic dimensions of a computing domain is on the order of a few wavelengths in size. However, extreme communication speeds, wireless access points closer to the user and smaller pico and femto cells will require increased accuracy in predicting and planning wireless signals, testing the accuracy limits of the ray tracing methods. The increased computing capabilities and the demand for better characterization of communication channels that span smaller geographical areas make numerical full-wave techniques attractive alternative even for larger problems. The paper surveys ways of overcoming excessive time requirements of numerical full-wave techniques while providing acceptable channel modelling accuracy for the smallest radio cells and possibly wider. We identify several research paths that could lead to improved channel modelling, including numerical algorithm adaptations for large-scale problems, alternative finite-difference approaches, such as meshless methods, and dedicated parallel hardware, possibly as a realization of a dataflow machine

Accurate and efficient full-wave modelling for indoor radio wave propagation

The transition towards next-generation communication technologies has increased the need for accurate knowledge about the wireless channel. Knowledge of radio wave propagation is vital to the continued development of efficient wireless communications systems capable of providing a high data throughput and reliable connection. Thus, there is an increased need for accurate propagation models that can rapidly predict and describe the propagation channel. This is extremely challenging for indoor environments given the large variety of materials encountered and very complex and widely varying geometries.Currently, empirical or ray optical models are the most common for indoor propagation. Empirical models based on measurement campaigns provide limited accuracy, are very costly and time-consuming but provide rapid predictions. Deterministic models are applied to the geometrical representation of the environment and are based on Maxwell’s equations. They can produce more accurate predictions than empirical models. Ray tracing, an approximate model, is the most popular deterministic model for indoor propagation. The current trend of research is focused on improving its accuracy. Full-wave propagation models are based on the numerical solution of Maxwell’s equations. They are able to produce accurate predictions about the wireless channel. However, they are very computationally expensive. Thus, there has been limited attempts at developing indoor propagation models based on full-wave techniques. In this work, the Volume Electric Field Integral Equation (VEFIE) is used as the basis of a full-wave indoor propagation model. The 2D and 3D formulations of the VEFIE are applied to model the propagation of radio waves indoors. An enhancement to the 2D VEFIE, called 2D to 3D models, is developed to improve its accuracy and utilise its efficiency. It is primarily used for the prediction of time domain characteristics due to its high efficiency whereas the 3D VEFIE is shown to be suitable for frequency domain predictions

Characterization of the Spatial Distribution of the Electric Field Strength in Indoor Propagation at 2.45 GHz

Small-scale spatial variations of the electric field strength or “fast fading” are encountered in indoor environments, and are of particular concern for indoor wireless communication applications as well as for electromagnetic compatibility assessment. This thesis is motivated by the problem of electromagnetic interference with a critical-care medical equipment caused by fields radiated by portable electronic devices such as cell phones and tablet computers. Measurement and computer simulation of the electric field strength, in both controlled and real-world scenarios, are explored to estimate parameter values of statistical models for the fast fading in a region of interest inside a building. First, a method for measuring the dielectric constant of wall construction materials is developed for two reasons: little information available on electrical properties of such materials in the frequency range of interest, 2.4 GHz ISM band, and variations in material properties caused by different manufacturing processes employed by different manufacturers. The proposed technique, referred to as the parallel-path method, falls into the category of free-space methods and is shown to be more sensitive to the dielectric constant than free-space methods based on normal incidence only. Having determined the dielectric constant of gyproc slabs and of a wooden door, a controlled multipath environment is built inside an anechoic chamber. Two line-of-sight and a non-line-of-sight scenarios, each with about 4000 measurement points, are studied. We apply the Friedman’s goodness-of-fit test at 5% significance level to show that a ray-tracing technique based only on 3D geometrical optics is suitable for estimating the fast fading of the electromagnetic field at 2.45 GHz in a very controlled situation. Then the Anderson-Darling goodness-of-fit test, also at 5% significance level, is applied to show that in the vicinity of a transmitter the Ricean, Normal, Nakagami, and Weibull distributions can be equivalently used to represent the spatial fast fading for both line and non-line-of-sight scenarios. Furthermore, the effects of metal studs are shown to worsen not only point-by-point agreement between measurement and GO simulation, but also the agreement on the statistics of the fast fading in a 65 by 65 cm region. Another aspect of this thesis is the development of a new method for estimating the parameters of the Ricean probability density function. This new method is compared to the maximum-likelihood method, and is shown to provide accurate estimates with samples containing as few as 36 data points for regions within 2 m from a transmitter, and as few as 9 data points for regions farther away. This is a considerable improvement in term of computation time when compared to estimates based on approximately 4000 points, or even 200 data points. Together with GO simulations, this method reduces the initial and elaborated measurement approach to only a few simulated points and a statistical model. Finally, this methodology is extended and applied to real-world scenarios such as a long hallway and a conventional laboratory room. The agreement between measurement and GO simulation is not as good as that of the experiment conducted in a shielded anechoic chamber, but it is still reasonable, especially because the interior structures of walls such as metal studs are not modeled by the GO code. As for the statistical models used to describe the electric field strength variation in a region, it is shown that the Ricean, Normal, Nakagami, and the Weibull distributions can be employed. However, for the data collected in this work, the Normal distribution is the one that results in the worst fit to measured data for most of the cases. It is demonstrated that, even though diffracted rays are not taken into account, GO simulation allows for an accurate estimation of the parameters of a statistical model for the fast fading, for both controlled and most real-world scenarios, provided that the site geometry and electrical properties of walls, floor, and ceiling are known

Wideband mobile propagation channels: Modelling measurements and characterisation for microcellular environments

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Study of Dual Band Wearable Antennas Using Commonly Worn Fabric Materials

In recent years, body-centric communication has become one of the most attractive fields of study. The versatile applications of body-centric communication not only being used for health monitoring, but also for real-time communication purposes in special occupations. They are important for supporting a population with increasing life expectancy and increase the probability of survival for the people suffering from chronic illness. For both wearable and implantable form of body-centric communication, characterizing the system electromagnetically is very important. Given the constraints in power, size, weight and conformity, one of the most challenging parts become the designing antenna for such communication systems. Wearable antennas are the most popular option regarding these issues. Wearable antennas are easier and simpler to mount on clothing when they are made of textile materials. In the process of designing a textile antenna, the availability of the fabrics is pivotal to mount on regularly worn clothes. In this report, several designs of a co-planar waveguide microstrip patch antenna are presented. Instead of felt fabric, the antenna was modified using 100% polyester and cotton fabric for the substrate material. A parasitic patch slot was created on the co-planar ground plane to achieve the dual band resonance frequencies at 2.4 GHz and 5.15 GHz. The geometrical modifications of the antennas were described and their performances were analyzed. The antenna achieved resonating frequency with a thinner substrate as the dielectric constant went higher for the fabrics. The design with different fabric materials was first simulated in CST Microwave Studio, then fabricated and measured in a regular environment. They were also mounted on a 3-D printed human body model to analyze the bending effect. The design of the antennas shows satisfactory performance with a good -10dB bandwidth for both the lower and higher desired resonating frequency bandElectrical Engineerin